Permanent magnet rotor synchronous motor

ABSTRACT

A synchronous self-starting timer motor having a disc shaped rotor with an annular ring of permanently magentized poles about the pheriphery therof. The magnetized poles are of alternately opposite polarity with the magnetic fields generated thereby being substantially perpendicular to the plane of the rotor. The stator includes a core having at least one pole pair which defines an axial air gap through which the magnetized annular pole portion of the rotor passes. The stator also has an energizing winding which induces an alternating or pulsating flux field in the core of the stator which field co-acts with the field of the rotor to drive the rotor at a speed proportional to the frequency of the flux field. The rotor has a low moment of inertia, is light in weight and has a large magnetic working area so that the synchronous motor is capable of generating high torque at a low input power level.

United States Patent 1191 Ingenito PERMANENT MAGNET ROTOR SYNCHRONOUSMOTOR [75] Inventor: Michael J. Ingenito, New York,

[73] Assignee: General Time Corporation, Mesa,

Calif.

[22] Filed: Feb. 17, 1972 [21] Appl. No.: 227,072

[52] US Cl 310/156, 310/162, 310/163,

[51] Int. Cl. H02k 21/12 [58] Field of Search 310/46, 156, 162-164,

[56] References Cited UNITED STATES PATENTS 2,993,159 7/1961 DeVol310/268 X 3,576,455 4/1971 lngenito 310/163 3,678,311 7/1972 Mattingly310/156 3,541,778 11/1970 lngenito et a1 310/46 X 3,231,770 l/1966 Hyde310/156 3,304,449 2/1967 Pohlman et al 310/268 X 3,355,645 1l/1967Kawakami et a1. 310/156 X [11] 3,803,433 1 Apr. 9, 1974 FOREIGN PATENTSOR APPLICATIONS 1,177,523 l/1970 Great Britain 58/23 A PrimaryExaminer-D. F. Duggan Attorney, Agent, or Firm-Pennie & Edmonds [5 7]ABSTRACT A synchronous self-starting timer motor having a disc shapedrotor with an annular ring of permanently magentized poles about thepheriphery therof. The magnetized poles are of alternately oppositepolarity with the magnetic fields generated thereby being substantiallyperpendicular to the plane of the rotor. The stator includes a corehaving at least one pole pair which 10 Claims, 7 Drawing FiguresPATENTEDAPR ,9 I574 SHEET 2 [IF 2 FIG. 5.

PERMANENT MAGNET ROTOR SYNCHRONOUS MOTOR BACKGROUND OF THE INVENTIONThis invention relates to synchronous electric motors and, morespecifically, to very inexpensive self-starting synchronous motorshaving high efficiency while requiring low power input. One use of theself-starting synchronous motor of this invention is for drivingcontinuously a digital or direct read clock mounted in an automobiledashboard wherein the power input for the motor is from the customaryautomobile battery.

Synchronous timer motors have been used extensively in electric clocksfor some time because of the simplicity of such motors and the accuracyof the rotational frequency at the output thereof. Complementing this isthe fact that the typically low output torque of minature synchronousmotors is well suited to clocks which do not require high torqueoperating levels. In construction, prior timer or clock motors haveoften been exceedingly simple. The stator normally includes anenergizing winding in the form of a simple concentrically wound coilwhich surrounds part of a magnetic circuit, designated the core, whichdistributes the generated magnetic flux with respect to a rotor. Therotor structure has taken many forms'but can be a simple permanentmagnet disc polarized to have alternating north and south poles aboutits periphery. The rotor is rotatably positioned with respect to thestator core such that the stator core and the rotor define a radial airgap through which the flux induced in the core passes. Because of thesimple structure of such synchronous timer motors, they are easilymanufactured and produced in large numbers resulting in a very low costper unit. These motors, however, have been notoriously inefficient. Forexample, the efficiency of prior timer motors has normally beenless'than 1 percent, although, in some of the better grade motors havinga more complex structure, the efficiency has been 2 percent or greater,an example of which is the motor disclosed in U.S. Pat. No. 3,469,131,issued Sept. 23,

1969 and which is assigned to the same assignee as is v the presentapplication. However, the motorof the stated patent is relativelyexpensive and for the same volume or size, does not have the torquecapabilities as the motor disclosed herein.

Over the years battery powered clocks have been developed and are nowvery popular. These clocks generally operate by sustaining thereciprocating or oscillatory motion of a balance wheel, tuning fork, orpendulum which in 'tum mechanically drives the hands of the clock. Asimple low power transistor oscillator circuit is typically utilized tosustain the reciprocating or oscillatory motion and, consequently, thelow energy drain from the clock battery has permitted battery poweredclocks to operate for months without requiring a change of battery.

Synchronous motors such as disclosed in the aforementioned U.S. Pat. No.3,469,131, have been successfully used in battery powered clocks.However, as explained above, the motors are relatively expensive and donot have the capabilities necessary for rugged, low power applications.Accordingly, there has been a need for an efficient primary source ofrotational energy so that the need for converting reciprocating motioninto rotary motion can be eliminated. The converting of reciprocatingmotion to rotary motion involves added parts and steps in the assemblingprocess thereby resulting in added cost of producing timepieces. Evenmore costly and complex is the mechanism in automobile clocks forconverting intermittent reciprocating motion to a relatively smooth anduniform rotational motion. The use of this mechanism in automobileclocks has often resulted in automobile clocks keeping inaccurate timebecause the shock and the temperature and vibrational extremes normallyexperienced by the winding spring and associated parts of these clocksproduced nonlinear torque outputs. The motor of this invention with itsassociated electronics eliminates the complex horology features ofpresent automobile clocks such as, the hairspring, the balance wheel,the main spring rewind mechanism, etc. Moreover, this motor provides thetorque necessary to drive displays other than conventional indicatinghands, such as, for example, digital clock drums.

It therefore is an object of this invention to provide a simple, andefficient synchronous motor for powering battery operated clocks.

It is another object of this invention to provide an efficient,continuously operating source of rotational energy for automobile clocksin which the source of rotational energy is a self-starting synchronoustimer motor which requires a low input power level.

SHORT STATEMENT OF THE INVENTION Accordingly, this invention relates toan efficient synchronous motor for producing a relatively large outputtorque at a low power input level. The motor includes a stator having acore with at least one pole pair and an energizing winding coupled tothe core to generate an alternating or pulsating flux field in the corefor rotationally driving a rotor. The rotor is a disc having an annularring of pennanently magnetized poles about the periphery thereof. Themagnetized poles are of alternately opposite polarity with the magneticfields generated thereby being directed substantially perpendicular tothe plane of the disc and parallel to the flux lines induced in thestator core by the stator windings. The annular magnetized portion ofthe rotor passes through an axial air gap which is defined by the statorpole pair. The rotor has a-low moment of inertia and is lightweight withthe magnetized portions thereof providing a large magnetic working areahaving a high retentivity. Consequently, the motor is capable ofgenerating a high torque at a low power input level.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantagesof this invention will be more fullyunderstood from the followingdetailed description of the preferred embodiment, the appended claimsand the accompanying drawings in which:

FIG. 1 is a plan view of the self-starting synchronous timer motor ofthis invention showing the rotor positioned in an axial air gap definedby the stator core;

FIG. 2 is an end view of the synchronous motor showing the annularmagnetized portion of the rotor;

FIG. 3 is a perspective view of the rotor illustrating the annular ringof magnetic poles at the outer periphery thereof;

FIG. 4 is a partial plan view of the rotor and stator assembly showingthe relative endwise configuration of the stator with respect to therotor;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Refer now to FIG. 1which shows the preferred embodiment of the self-starting synchronousmotor of this invention. The stator 11 includes a core 13 and anenergizing winding 21. The core 13 includes two complementary annealediron plates 15 and 17 which are preferably formed by a stamping process.In order to conserve space and to provide more efficient coupling withrespect to energizing winding 21, the winding support legs 16 of thecore plates 15 and 17 are offset with respect to each other as is moreclearly illustrated in FIG. 2. The legs are positioned side-by-side andare spot welded to form a unitarystator core. Since the leg portions ofthe core are positioned side-by-side, the cross sectional area of thecore as it passes through the winding 21 has a square configurationwhich, as is wellknown, provides a very efficient electromagneticcoupling relationship with the winding 21. The other portions of thestator core outside of the winding 21 need not be as thick as thecombined leg portions 16, and the optimum thickness of the stator in allareas other than the leg portions can be determined by techniques wellknown to those skilled in the art from a knowledge of the leakage fluxat the pole faces of the stator core, the surface area of the rotorpoles, the air gap between stator pole pairs, and the unmagnetizedtransition region between the adjacent north and south poles of the r0.-

tor.

A winding bobbin 19 comprised of any suitable material such as ahardened plastic material is supported by the winding support legs 16.The energizing winding 21 is concentricallywound about the bobbin and inthe preferred embodiment is comprised of 6,000 turns of 43" gage, copperwire having a total resistance of approximately 860 ohms. It should beunderstood, however, that the number of turns and the wire gage used maybe of any suitable number and type depending on the number of statorpole pairs, the torque required,

and theoperating voltage range. Electrical current is coupled to thewinding 21 via leads 23.

The end portions of the stator core passing outside of the winding 21are separated to form an axial air gap 27 for the rotor 25. The size ofthe air gap depends on the thickness of the rotor and the DC magneticstiffness desired. Thus, ordinarily it is desirable to make the air gaplarge for manufacturing ease but, as will be seen The rotor is a dischaving a thickness of approximately 0.023 inches and consists ofa lowdensity material such as barium ferrite in a rubber binder which iscommonly sold under the trade name Plastiform and which is relativelyinexpensive in the sizes required for the rotor. The residual inductionvalue, i.e., retentivity of Plastiform, is 0.22 webers per meter which,as will be seen hereinbelow, is of importance to the operatingcharacteristic of the motor of this invention. As shown in FIG. 2, anannular ring about the outer periphery of the rotor is permanentlymagnetized through the thickness of the rotor to form an annularmagnetic working area on both sides of the rotor. The magnetized areaincludes truncated triangular sections called rotor poles which are ofalternately opposed polarity as can be most conveniently seen in FIG. 3.The poles are positioned so that they are contiguous to one anotherabout the periphery of the rotor thereby rendering the entire annularring available for generating alternately opposed magnetic fields. Therotor is mounted on an axial shaft 29 for rotation with respect to thestator by any suitable means known in the art. In the preferredembodiment there are 16 rotor poles and the energizing winding 21 isexcited with a current having a frequency of 64 Hz. Accordingly, therotor is driven at 8 cycles per second.

The aforementioned synchronous motor is of exceedinglysimple yet ruggedconstruction suitable for rapid mass production and for use invibrational environments such as in automotive vehicles. As will beexplained hereinbelow, since the rotor density is low, while at the sametime having a large magnetic working area, the ratio of the moment ofinertia of the rotor to the torque developed by the motor is low,thereby rendering the motorcapable of self-starting. A simple no-backdevice cooperating with the gear train (not shown) is employed to insurerotation of the rotor in the desired direction. Such devices are verywellknown in the art to which this invention pertains.

The operation of the motor is according to wellknown principles ofsynchronous motors. Briefly, with the rotor positioned as shown in FIG.2 and assuming it is rotating counter clockwise, the stator core passesa magnetic-flux field throughthe rotor such that the north magnetic pole31 is attracted to the stator pole pair. At the same time the southmagnetic pole 33 is repulsed, in the counter clockwise direction awayfrom the stator pole pair. A fraction of a second later and after l/l6thof a complete rotation of the rotor, the magnetic field in the stator isreversed and the south magnetic pole 35 of the rotor is attracted to thestator pole pair and the north magnetic pole 31 is repulsed in thecounter clockwise direction away from the stator. Thus, the stator poleis continuously driven by the interaction of the alternate polaritymagnetic fields of the rotor and the alternating magnetic field in thestator. It should be understood that a pulsating unipolar magnetic fluxfield could also be generated in the stator. In such a case, the rotornorth pole 31 would be attracted and the rotor south pole 33 repulsedwhen a unipolar pulse is coupled to winding 21. A fraction of a secondtion rather than every 1/ 1 6th of a revolution, the movement, of therotor will be less smooth when excited by a unipolar pulsating magneticfield than when excited with a typical AC flux field.

The developed torque required to self-start a permanent magnetsynchronous motor must be greater than the static friction torque plusthe stiffness torque due to the permanent magnet plus the inertia torqueof the rotor. The low density of the rotor material obviously reducesthe friction and inertia torque and the permanent magnet stiffnesstorque can be adjusted to the appropriate value depending on thespecific use requirements of the motor. The average torque that can bedeveloped by such a motor is proportional to the product of the magneticfield due to the impressed current in the windings and that due to thepermanent magnets in the rotor. Both of these torques are dependent onthe characteristics and geometry of the magnet path through the rotor,stator and the air gap separating the rotor and stator. Since the rotorof this invention is thin and has alow moment of inertia and yet has alarge magnetic working area, the motoris able to develop a large torqueat low power input levels and at the same time requires relativelylittle starting torque when compared with prior art motors. The maximumtorque required to self-start the synchronous motor of this inventioncan be shown to be:

where T, is the required torque, J isthe moment of inertia of the rotor,f is the frequency of the current cou' pled to the energizing windings,and P, is the total number of rotor poles. It thus can be seen that themoment of inertia J should be held to a minimum in order to reduce thetorque required for self-starting. v

The proper expression for the moment of inertia of the rotor shown inFIG. 3 is:

where D is the density of the rotor material, L, is the thickness of therotor magnet and A, is the total surface area of one side of the rotordisc. Substituting equation (2) into equation (1) the following equationis derived:

T, s D L, A, 1 /1,

T P, P, (L L,) d), ,/4 MOA,

where T, is the maximum torque that can be developed by the motor, P, isthe number of stator pole pairs, L, is the air gap length, d, is thepeak value of the magnetic flux in the air gap that is generated by theimpressed current, 45, is the maximum net magnetic flux in the air gapgenerated by the permanent magnets of the rotor, M0 is the permeabilityof free space and A, is the cross sectional area of a single stator orrotor pole. It should be noted that the aforementioned formula isaccurate provided that the stator iron does not become saturated, theflux in the air gap varies sinusoi dally, and the gear train backlash ofthe associated clock is such that the motor is brought to synchronousspeed before any load torque is reflected back to the rotor. Inaddition, it is assumed that the stator pole faces have the samegeometric configuration as the rotor poles and that fringing effects areneglected. These conditions are typical of present day clock gear trainsand of synchronous motors.

The flux expressions in equation (4) should be converted to expressionsof current in order for equation (4) to be meaningful in terms of inputpower and efficiency. Thus, equation (4) can be rewritten as:

T,, 0.16 P, NI A R (L,/L, L,,)

where N is the number of turns in the energizing winding 21, I is themaximum current coupled thereto, A,

is the total annular area of the permanent magnet poles, i. e., themagnetic working area, and R is the residual induction value of thePlastiform rotor material which is 0.22 webers per meter? Since thedeveloped torque is proportion to the magnetic working area A it isimportant that this area be made as large as possible such as by makingthe sides of each magnetic rotor pole contiguous with its neighbors.

Since the maximum average developed torque has to be equal to or greaterthan the maximum average required torque, equations (3) and (5) areequated to determine the required current.

Equation (6) can now be applied to the synchronous motor illustrated inFIGS. 1-3 by assuming the following values for the parameters of theequation:

P, 16 L, IO meters A, 1.26 X 10 meters 2 A, 0.79 X 10 meters where R isthe total resistanceof the winding which is approximately 860 ohms, P isthe power loss in the core due to hystersis and eddy currents and isestimated to be approximately 50 microwatts, and P is the power output.Accordingly, the power input can be computed and is P, 6.07 47.6 0.0553.72milliwatts The efficiency can now be computed and is:

E P,,/P.,, 100%: 6.07/53.72 100% 11.3%

As can be seen the synchronous motor not only can develop sufficienttorque for self-starting, but the efficiency thereof is a substantialimprovement over the 1% efficiency levels of prior art simplifiedsynchronous timer motors. 1f the motor is not required to beselfstarting, as for example, in the case where the motor is started byhand, the high starting torque is not required and hence very low poweroperation is possible.

It can be seen from equation (6) that if the number of stator poles isincreased, the maximum input current required is reduced. Assume, 'forexample, that the number of stator poles is increased to eight. Applyingthe above formula, the maximum required input current can be found to be1.31 milliamperes and the developed torque can be found to be 8.84ounce-inches. Since the power output is the product of torque developedand the angular speed of the rotor, the power output P is found to be6.07 milliwatts which is the same as in the case where the stator hasonly one pole pair. Assuming the coil resistance to be 860 ohms, theinput power to supply the copper losses is 0.744 milliwatts and the corelosses will be approximately times higher than in the one statorpolecase. Thus the total input power P, can be computed by equation (7)and is 7.31 milliwatts. The efficiency according to equation (8) is:

, E= P /Pl 100% 6.07/7.31 (100) 83.1%

Thus by increasing the number of stator poles, the efficiency of thesynchronous motor is substantially increased.

Refer now to FIG. 4 which is a partial end view of the stator showingthe configuration of the stator pole face with respect to the magnetizedportion of the rotor. As shown the stator portion 18 is in the form of atruncated triangle. this configuration most nearly matches theconfiguration of the permanently magnetized pole faces of rotor 25. Theupper leg portion 18 of the stator extends downward to the lower legportion 16 thereof with the windings 21 not shown. The leg 16 of plate17 of the stator is shown and as aforementioned is spot welded to plateto form a unitary stator. It should be understood that while theaforementioned equations were developed with respect to a stator polehaving the configuration shown in FIG. 4, the stator poles, also, canhave a rectangular configuration as illustrated most clearly in FlG. 2.The rectangular pole face construction requires fewer steps inmanufacturing the stator thereby reducing the cost of the motor while atthe same time the characteristics of the motor including efficiency arenot substantially adversely affected by such a-modification in thestator pole configuration.

Refer now'to FIG. 7 where there is shown a schematic diagram of a drivecircuit for providing AC energization to the winding 21 of thesynchronous motor. The circuit is comprised of three fundamental parts,

namely, a crystal controlled oscillator designed by the numeral 47,a'divider circuit 49 and a drive circuit 51. DC power is coupled to thecircuit via resistor 43 which provides transient current protection foreach of the three components of the circuit. A Zener diode 45 is coupledbetween the low voltage end of resistor 43 and a reference potentialsuch as ground. A second DC source 53 is coupled to the divider anddrive circuits for providingthe appropriate bias potential thereto.

The oscillator circuit includes a quartz crystal 55 which is designed tooscillate at 262,144 Hz. Quartz crystals are well-known and are readilyavailable commercially. The crystal 55 is connected at one side thereofto the input of an amplifier 57 and the other side thereof is coupled tothe output of the amplifier via a variable capacitor 59. The input ofamplifier 57 is also connected to reference potential via a fixedcapacitor 61 and the output of the amplifier is coupled to referencepotential via fixed capacitor 63. A biasing resistor 65 is connectedbetween the input and output terminals of amplifier 57 and biases theamplifier 55 in its active region to initiate oscillation of oscillator47. Variable capacitor 59 operates to vary the resonant frequency of thecrystal oscillator thereby varying the frequency at the output ofamplifier 57. The output ofthe amplifier 57 which is 262,144 Hz isconnected to a buffer amplifier 67 which preferably has a high inputimpedance so that operation of the divider stage 49 does not adverselyaffect the frequency of the output of the oscillator 47. The output(C-MOS) buffer amplifier 67 is connected to divider 49 which includes aplurality of binary divider stages. lnthe preferred embodiment thedivider 49 includes twelve serially connected flip-flops whichdivide'the output of the crystal oscillator down to 64Hz. The output ofthe divider is connected to adrive circuit 51 which provides an outputcurrent on the order of several milliamperes for energizing the windings21. The divider circuit 49, the drive circuit 51, buffer amplifier 67and the amplifier 57 are formed on an integrated circuit chip commonlyknown as a'complementary metal oxide semi-conductor C- MOS) byintegrated circuit techniques well known in the art.'The circuitillustrated in FIG. 7 provides not only a highly stable 64 Hz output fordriving windings 21 but also requires very little power from the DCsource of energy. Refer now to FIG. 5 where there is shown a crosssectional view of a multi-stator pole self-starting synchronous motor.The stator includes a core portion comprising a pair of legs 71 and 73with a cylindrical connecting arm 75 separating each of the legs. Theconnecting arm 75 consists of a soft iron material and has a holetherethrough through which a bolt extends for securing the connectingarm to the legs 71 and 73. The legs 71 and 73 are bent inwardly towardeach'other proximate the rotor 77 with each of the legs having alignedholes for permitting the rotor spindle or shaft 89 to pass therethrough.A bushing 79 is positioned in each hole. A pair of complementary statorpole pieces each having eight pole faces thereon are mounted on eachbushingwith the pole faces of the pole pieces being directed toward eachother as shown in FIG. 5. A pole piece is shown in perspective in FIG.6. A hole 81 extends through the center thereof into which is positioneda bushing 79. At the external periphery of the pole piece are aplurality of pole faces 84 extending upwardly away from the base portionof the pole piece. Each of these faces are separated by a notchedportion 83. The pole faces, as shown, take the form of a truncatedtriangle having the same general configuration as the magnetized portionof the rotor shown in FIG. 4.

The stator is supported by means of a pair of brackets 85 which consistof a non-magnetized material. The pole pairs 78 are separated or spacedwith respect to each other by means of a pair of spacers 87 positionedbetween the legs 71 and 73 of the stator and are se-.

cured in place by a pair of bolts extending through the brackets 85, thelegs 71 and 73, and the spacers 87. A rotor 77 is positioned between thepole pairs 78 with an axial air gap separating the rotor from the polepairs. The rotor is mounted on a spindle 89 which is journaled forrotational motion in the frame of the motor 91. Axial bearings 93 permitrelatively frictionless rotational movement with respect to brackets 85and axial bearings 94 permit'relatively frictionless movement of thespindle 89 with respect to bushings 79.

In operation the multi-stator rotor of FIG. 5 attracts and repels therotor poles in the same manner as the single stator pole rotor exceptthat more stator poles are now attracting and repelling thecorresponding rotor poles thereby generating a larger torque output.

The synchronous motors described herein are particularly well adaptedfor driving automobile clocks since they are of simple yet ruggedconstruction thereby rendering the motors amenable to mass productiontechniques. Further, since the synchronous motors provide directrotational energy to'a clock gear train, the intermittent reciprocal torotational motion converting mechanism normally required in automobileclocks which is susceptible to ambient temperature variations and shockis not required thereby providing a more accurate automobile clock.Finally, the increased efficiency of these motors permits their use inautomobiles without concern that the battery might be drained of energyby the motor. While several embodiments of the self-starting synchronousmotor have been described, it is within the contemplated scope of thisinvention that numerous changes can be made in the embodiment describedwithout departing from the spirit and scope of the invention as definedby the appended claims.

I claim:

I. A synchronous motor comprising:

I a disc shaped rotor comprised of a low density material of highretentivity and havinga low moment of inertia and a large magnetic areato provide a high output relative to the moment of inertia thereof, saidmagnetic area including an annular ring of permanently magnetized polesextending through the thickness and about the periphery thereof, each ofsaid poles being magnetized axially and having a pole of oppositepolarity positioned contiguously on each side thereof, and

a stator including a core and an energizing winding,

said core having at least one pole pair which defines an axial air gapthrough which passes the permanently magnetized annular portion of saidrotor, said energizing winding being coupled to said stator core forproviding an energizing altemating flux field in said core, said fluxfield passing between said stator poles through said rotor substantiallyperpendicular to the plane of said rotor, the mag netic fields generatedby said rotor poles passing through said stator substantiallyperpendicular to the surface of said stator pole pair.

2. The motor of claim 1 wherein said annular magnetized poles of saidrotor are integral with said rotor.

3. The motor of claim 2 wherein the rotor material consists of bariumferrite powder mixed with a low density binder.

4. The motor of claim 2 wherein said stator has only one stator polepair.

5. The motor of claim 2 wherein said stator core includes a pair ofcomplementary pole pieces, said pole forming a plurality of pole pairswith each pole pair having the approximate configuration of said rotorpoles.

6. The motor of claim 5 wherein said pole faces are aligned co-axiallywith said rotor and are rigidly secured to said stator core.

7. A battery operated self-starting synchronous timer motor for poweringan automobile clock comprising:

a disc shaped rotor comprised of a low density material of highretentivity and having a low moment of inertia and a large magnetic areato provide a high output relative to the moment of inertia thereof, saidmagnetic area including an annular ring of permanently magnetized polesextending through the thickness and aboutthe periphery thereof, each ofsaid poles being magnetized axially and having a pole of oppositepolarity positioned contiguously on each side thereof; and statorincluding a core and an energizing winding, said core having at leastone pole pair which defines an axial air gap through which passes thepermanently magnetized annular portion of said rotor, said energizingwinding being coupled to said stator I core for providing an energizingalternating flux field in said core, said flux field passing betweensaid stator poles through said rotor substantially perpendicular to theplane of said rotor, the magnetic fields generated by said rotor p'olespassing through said stator substantially perpendicular to the surfacesof said stator poles.

8. The motor of claim 7 wherein said annular magnetized poles of saidrotor are integral with said rotor.

9. The motor of claim 8 further comprising circuit means for providingan AC energizing signal to said energizing winding, said circuit meansincluding a crystal controlled oscillator, a frequency divider means fordividing the frequency of the output of said oscillator, and drive meansresponsive to said divider means for energizing said windings. I

10. The motor of claim 8 wherein said stator core includes a pair ofcomplementary pole pieces, said pole pieces forming a plurality of polepairs with each pole pair having the approximate configuration of saidrotor poles.

Q I UNITED STATES PATENT swim I Q CERTEFICATE 0F CURRECTION Patent No 3803 433 Dated April "9 l 1974 Inventor (A) Michael J. Inqenito It iscertified that error appears in the above-identified patent I and thatsaid Letters Patent are hereby correctec'l as shown below:

Column 5, in the formula following line 60, "125 should be 6 Column 7,line 51, "this" should be -This- Column 8, line 34, delete "(C-MOS) andinsert -of- Column 8, line 45, before "C- insert a parenthesis Column10, (claim 5) line 18, after "pole" insert --.pieces--.

Signed and sealed this 22nd day of October 1974,

(SEAL) Attest:

McCoy M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM Po-mso (10-69) r r USCOMWDC floflmpw U. 5. GOVERNMENTPRINTING OFFICE 1959 0-3664.

UNITED STATES PATENT OFFICE CERTEFICATE GF CQRRECTION Patent No.3,803,433 Dated April 9, 1974 Inventor) Michael J. Increnito It iscertified that error appears in the above-identified patent I and thatsaid Letters Patent are hereby corrected as shown below:

, Column 5, in the formula following line 60, 3 should be Column 7, line51, "this" should be --T'his-- Column 8, line 34, delete "(C-MOS) andinsert --of-- Column 8, line 45, before "0-" insert a parenthesis IColumn 10, (claim 5) line 18, after "pole" insert pieces-.

Signed end Sealed this 22nd day of October 1974,

(SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer I Commissioner ofPatents 1 FORM Po-1os0 (10-69) v USCOMWDC 603mm 0.3 GOVERNMENT PRINTINGOFFICE I969 0-386-534,

1. A synchronous motor comprising: a disc shaped rotor comprised of alow density material of high retentivity and having a low moment ofinertia and a large magnetic area to provide a high output relative tothe moment of inertia thereof, said magnetic area including an annularring of permanently magnetized poles extending through the thickness andabout the periphery thereof, each of said poles being magnetized axiallyand having a pole of opposite polarity positioned contiguously on eachside thereof, and a stator including a core and an energizing winding,said core having at least one pole pair which defines an axial air gapthrough which passes the permanently magnetized annular portion of saidrotor, said energiZing winding being coupled to said stator core forproviding an energizing alternating flux field in said core, said fluxfield passing between said stator poles through said rotor substantiallyperpendicular to the plane of said rotor, the magnetic fields generatedby said rotor poles passing through said stator substantiallyperpendicular to the surface of said stator pole pair.
 2. The motor ofclaim 1 wherein said annular magnetized poles of said rotor are integralwith said rotor.
 3. The motor of claim 2 wherein the rotor materialconsists of barium ferrite powder mixed with a low density binder. 4.The motor of claim 2 wherein said stator has only one stator pole pair.5. The motor of claim 2 wherein said stator core includes a pair ofcomplementary pole pieces, said pole forming a plurality of pole pairswith each pole pair having the approximate configuration of said rotorpoles.
 6. The motor of claim 5 wherein said pole faces are alignedco-axially with said rotor and are rigidly secured to said stator core.7. A battery operated self-starting synchronous timer motor for poweringan automobile clock comprising: a disc shaped rotor comprised of a lowdensity material of high retentivity and having a low moment of inertiaand a large magnetic area to provide a high output relative to themoment of inertia thereof, said magnetic area including an annular ringof permanently magnetized poles extending through the thickness andabout the periphery thereof, each of said poles being magnetized axiallyand having a pole of opposite polarity positioned contiguously on eachside thereof; and a stator including a core and an energizing winding,said core having at least one pole pair which defines an axial air gapthrough which passes the permanently magnetized annular portion of saidrotor, said energizing winding being coupled to said stator core forproviding an energizing alternating flux field in said core, said fluxfield passing between said stator poles through said rotor substantiallyperpendicular to the plane of said rotor, the magnetic fields generatedby said rotor poles passing through said stator substantiallyperpendicular to the surfaces of said stator poles.
 8. The motor ofclaim 7 wherein said annular magnetized poles of said rotor are integralwith said rotor.
 9. The motor of claim 8 further comprising circuitmeans for providing an AC energizing signal to said energizing winding,said circuit means including a crystal controlled oscillator, afrequency divider means for dividing the frequency of the output of saidoscillator, and drive means responsive to said divider means forenergizing said windings.
 10. The motor of claim 8 wherein said statorcore includes a pair of complementary pole pieces, said pole piecesforming a plurality of pole pairs with each pole pair having theapproximate configuration of said rotor poles.